Examples

        %= panel

        <div class="panel panel-default">
            <div class="panel-body">
            </div>
        </div>

The class is set to `.panel-default`, by default.

        %= panel undef ,=> begin
            <p>A short text.</p>
        %  end

        <div class="panel panel-default">
            <div class="panel-body">
                <p>A short text.</p>
            </div>
        </div>

If you want a panel without title, set the title to `undef`.

A short text.

        %= panel 'The Header' => begin
            <p>A short text.</p>
        %  end

        <div class="panel panel-default">
            <div class="panel-heading">
                <h3 class="panel-title">The Header</h3>
            </div>
            <div class="panel-body">
                <p>A short text.</p>
            </div>
        </div>

### The Header

A short text.

        %= panel 'Panel 5', success, begin
            <p>A short text.</p>
        %  end

        <div class="panel panel-success">
            <div class="panel-heading">
                <h3 class="panel-title">Panel 5</h3>
            </div>
            <div class="panel-body">
                <p>A short text.</p>
            </div>
        </div>

### Panel 5

A short text.

        %= panel

        <div class="panel panel-default">
            <div class="panel-body">
            </div>
        </div>

        %= panel undef ,=> begin
            <p>In the panel.</p>
        %  end

        <div class="panel panel-default">
            <div class="panel-body">
                <p>In the panel.</p>
            </div>
        </div>

In the panel.

        %= panel 'Test'

        <div class="panel panel-default">
            <div class="panel-heading">
                <h3 class="panel-title">Test</h3>
            </div>
            <div class="panel-body">
            </div>
        </div>

### Test

    %= panel 'The Header' => begin
        <p>A short text.</p>
    %  end

        <div class="panel panel-default">
            <div class="panel-heading">
                <h3 class="panel-title">The Header</h3>
            </div>
            <div class="panel-body">
                <p>A short text.</p>
            </div>
        </div>

### The Header

A short text.

        %= panel 'Panel 5', success, begin
            <p>A short text.</p>
        %  end

        <div class="panel panel-success">
            <div class="panel-heading">
                <h3 class="panel-title">Panel 5</h3>
            </div>
            <div class="panel-body">
                <p>A short text.</p>
            </div>
        </div>

### Panel 5

A short text.